Rodents have been exterminated by poisoned baits for many years. Such baits have taken the form of rodenticide-impregnated grains and other foods formed into small pellets or paraffinized blocks of various sizes. The blocks or pellets are usually placed on the ground, where rodents, having mistaken their find as serendipity, would consume the poisoned food.
Scattering pellets or blocks on the ground is problematic since animals other than the target rodents can eat the poisoned food. Additionally, the bait is easily scattered or carried away. Using larger paraffinized blocks can help prevent scattering. Such blocks are provided with external ridges to provide a better biting surface for the rodent, as shown in Sherman, U.S. Pat. No. 4,891,218, issued Jan. 2, 1990, which also shows a series of small holes running through the block to provide additional biting surface as the outside of the block is eaten await.
The Sherman patent further illustrates a recess provided on the underside of the block for mounting the block on an upright peg to prevent the rodent from carrying the block away. When used in elevated locations, such as rafters, trees or fences, it is also well known to nail the block in place in a vertical or horizontal position. This can aid in keeping it out of reach of non-target animals.
Bait blocks of this type have been made by molding a mixture containing the rodenticide, the feed, and the binder (e.g. wax). Extrusion has also been used to make such products, as mentioned in Smith, U.S. Pat. No. 2,813,058, issued Nov. 12, 1957. However, when bait blocks are formed by extrusion, it is difficult to produce blocks with internal holes. Extrusion using a single orifice die cannot produce a product having an internal hole or recess. Such a hole or recess could be formed or drilled in a separate step after extrusion, but this would be inefficient and waste product. Molding the bait block makes it easier to form holes or recesses, but is slower and tends to waste more material than extrusion. Thus, there remains a need for a bait block configuration which has an internal hole to facilitate mounting and can be made by a simple extrusion process.